Since the early twentieth century, embryologists have known that much of early development is controlled by information in the cytoplasm of the egg. Maternal effect genes encode that information; their function is required during oogenesis for embryogenesis to occur. One means of studying the nature and function of maternal information is to isolate maternal effect genes. The DNA sequences thus isolated can be used as probes to study the molecular basis of interactions between the egg cytoplasm and the zygotic nucleus during embryogenesis. Caenorhabditis elegans, due to its defined cell lineage, physiology, and genetics, has been widely used for studies of early development. Several maternal effect lethal (mel) genes have been identified and characterized. These genes will be isolated by DNA transformation. In preliminary studies, the first important step in DNA transformation of C. elegans has been achieved: the introduction and propagation of foreign DNA. The next step is to demonstrate expression of the exogenously added sequences. Concomitantly, DNA will be isolated that corresponds to defined genetic regions surrounding and including mel genes. This DNA will be injected into mel mutants; complementation of the mutant defect will define DNA that encodes the gene. Once isolated, mel gene sequences can be used to identify and characterize RNA and protein products. The synthesis and metabolism of information encoded by mel genes will provide insights into how genes establish cytoplasmic information and then how the cytoplasm affects gene activity. This recursive interrelationship between cytoplasm and nucleus is a central issue in cellular behavior, development and differentiation. Thus, understanding these interactions has implications for the treatment of cellular and developmental defects and neoplasia.